1. Field of Invention
The present invention relates to a technology for reducing emission of NOx from an internal combustion engine of a vehicle into the atmosphere.
2. Description of Related Art
Recently a catalytic converter having a three-way catalyst is installed in an automobile for reducing emission of harmful air pollutants such as NOx, HC and CO contained in an exhaust gas discharged from an engine of the automobile. The three-way catalyst has a function that promotes reaction among those pollutants to generate harmless components such as N2, CO, and H2O.
It has been proposed to temporarily stop an internal combustion engine of the automobile during an operation of the automobile, for the sake of savings of energy resources and environmental protection, when certain conditions under which the engine is allowed or desired to be temporarily stopped are established. In fact, this technology which is called xe2x80x9ceco-runningxe2x80x9d has been implemented in some types of automobiles. The conditions for temporarily stopping the engine may be established when, for example, the vehicle stops at a red traffic light, or the vehicle stops or travels at a considerably low speed because of a traffic jam or the like. In a hybrid vehicle that is driven by a combination of an engine and an electric motor, the motor is operated to drive the vehicle by temporarily stopping the engine not only when the vehicle temporarily stops or travels at a considerably low speed but also when the vehicle travels in various operating states.
The catalytic converter including the catalyst for removing NOx in the exhaust system of the engine may cause a problem when the engine is temporarily stopped. The engine is generally stopped by discontinuing a fuel supply. The engine, however, will continue to be operated under the inertia for a while after discontinuing the fuel supply. During operation of the engine under the inertia, an oxygen-rich intake air is discharged into the catalytic converter that accumulates oxygen at every temporary stop of the engine. When the engine is started again in the aforementioned state, HC and CO flowing into the catalytic converter together with NOx will react with oxygen accumulated therein instead of causing the reaction between NOx and HC, CO to generate a harmless component N2. As a result, NOx is not removed and then discharged into the atmosphere.
The aforementioned problem is particularly critical for operating an eco-running vehicle or a hybrid vehicle in which the engine is frequently stopped and re-started.
In view of the foregoing problem, it is an object of the invention to provide a vehicle in which deterioration in a NOx removal function of the catalytic converter owing to oxygen accumulated therein upon an engine stop can be prevented while suppressing emission of HC, CO, and the like.
To accomplish the above and/or other objects, the invention provides a vehicle that includes a power-train including an engine, a motor at least temporarily connected to the engine, a battery serving to supply power to the motor, and a generator selectively driven by at least the engine to charge the battery; a catalytic converter that purifies an exhaust gas from the engine; and a controller that controls fuel supply to the engine, determines whether an engine stop condition for stopping the engine is established and whether an engine re-start condition for re-starting the engine is established, on the basis of a traveling state of the vehicle, and discontinues the fuel supply to the engine when it is determined that the engine stop condition is established, and controls an engine speed such that an amount of oxygen accumulated in the catalytic converter during an engine stop is adjusted to be within a preset range, and re-starts the fuel supply for driving the engine when it is determined that the engine re-start condition is established, while temporarily increasing an amount of fuel supplied to the engine.
An operation of the engine may be controlled such that the engine speed upon discontinuation of the fuel supply is within a preset range.
The fuel supply may be discontinued when a revolution phase of the engine is within a preset range.
The engine speed may be controlled after discontinuation of the fuel supply to the engine such that an amount of oxygen to be accumulated in the catalytic converter during an engine stop is controlled to a saturated amount of oxygen that can be accumulated in the catalytic converter.
An operation of the engine may be controlled such that a temperature of the catalytic converter upon discontinuation of the fuel supply is within a preset range.
When the engine is stopped by discontinuing the fuel supply, the catalytic converter accumulates oxygen fed from the engine that races under the inertia after the discontinuation of the fuel supply. The amount of oxygen accumulated in the catalytic converter, however, may be controlled to be within a preset range for reaction with an appropriate amount of HC fed into the catalytic converter by temporarily increasing the amount of the fuel supply. As a result, deterioration in the NOx removing function of the catalytic converter owing to oxygen accumulated in the catalytic converter may be prevented while suppressing emission of HC through the catalytic converter. The additional fuel may be supplied at the same timing as a normal fuel supply timing, or may be supplied at a different timing.
The amount of oxygen fed and accumulated into the catalytic converter while racing of the engine after discontinuation of the fuel supply is determined by an engine speed when a fuel supply is discontinued. Accordingly, if the engine speed upon start of discontinuation of the fuel supply is controlled to be within a preset range prior to the discontinuation of the fuel supply, the amount of oxygen to be accumulated in the catalytic converter upon the engine stop may be controlled within a preset range more accurately. The aforementioned control to adjust the engine speed into the preset range may be executed by controlling an intake air of the engine, driving the engine by the motor, and suppressing the engine operation by the generator.
The amount of oxygen fed and accumulated into the catalytic converter while racing of the engine after discontinuation of the fuel supply is determined by a revolution phase of the engine when the fuel supply is discontinued. Accordingly if discontinuation of the fuel supply is controlled to start at a timing when the revolution phase of the engine falls within the preset range, the amount of oxygen fed and accumulated into the catalytic converter resulting from the engine racing after discontinuing the fuel supply can be controlled to be within the preset range.
If the amount of oxygen accumulated in the catalytic converter is controlled to a saturated amount, the accumulated amount is determined in accordance with a temperature of the catalytic converter. The amount of the accumulated oxygen at the engine stop, thus, can be accurately derived from the temperature of the catalytic converter. Accordingly, the amount of the accumulated oxygen can be controlled to be within the preset range by controlling the catalytic converter temperature.
The amount of oxygen accumulated into the catalytic converter may be changed depending on the catalytic converter temperature. In case of a high catalytic converter temperature, the accumulated amount of oxygen is increased. Therefore, the accumulated amount of oxygen may further be accurately controlled to be within the preset range by controlling the catalytic converter temperature in addition to the engine speed control or the engine revolution phase control. The catalytic converter temperature may be controlled by performing control of either a fuel supply amount, an intake air supply amount, an ignition timing, or a combination thereof.